Signaling system for use in mine shafts



A ril 25, 1950 R. 1.. RUTHERFORD SIGNALING SYSTEM FOR USE IN MINE SHAFTS Filed Feb. 2'7, 1948 JNV TOR.

OMv-Q n w g xww 2 *M Patented Apr. 25, 1950 My .Jpresent'. invention hasjforits qbj'ectltojnrevide an improvedsignaling system ioruse in, mine shafts as a means of communication between the hoist operator and the operator .on the. cage. skip, during the-movement or .thelattelfirrespeotive of its position ol' depthJ-in theqsha, ,or conditions theremwhichmaycause variations; in the capacitance. between the cage and Walls. 'df th shaft.

Another objector myiinuelition is to-pr.ovide a signal system specially adapted for usefilnmine shafts which may be either vertical or inclined, and of open irregular .crossisection or trmbered and whichlby reason (if-surrounding conditions .due either tothe-presence of water may e d mp, or tothe nature .ofthe. stratapenetratecl. and materials handled on the .caeexmey be. dii ificult t maintainin a clean condition, either Qffwhich conditionssingly .or in, combination create (iii.- fioulties in maintainin prqper insulationof electrical conductors.

Moreovermy invention has as a pr',inc .p 1-0bject theutilization in conjunction with a-metal hoisting cable and the cage supportedithereou of a modulated radio. freque cy oscillator comprisinganoutput winding of .a transformencoil which is connected to separated points .on the cable whereby .the entire length of the cable becomes an autotransformer rendering'it possible. to. detect .the signals at the .hoist .ahove ground. and iIQPliO- duce them in a. suitable. receiver withoutfiiminutionanol .in.reality. at increased volumes when existing conditions in the shaft. increase. either the capacity vor conductance .between the wage andshait walls.

To these and other endsum .invelitiomcomprises further improvements. and, advanta es. .as will befurther .described in the .accempanying specification, the novelfeatures thereofheing set forth in the appended claims.

In the. drawings Figure lis a diagrammaticillustration showin a mine -shaft,.a hoist. andelevator-oable with .a cage or skip suspendedz-thereon there being an oscillator on the cage :anda radieirequencyie ceiver Qn'the. surface Withafl. pick-up 100p adjacent thecable.

Figure 2 is a diagrammaticview-illustratinge suitable .-form :of radio frequency "oscillator.

Figure 3 is asch'ematic illustration: "of carradi frequency receiving circuit.

.Similar reference -r.iume-ra1s,--in. theseveral-fieures,;indicate similar-parts.

-.In the minin industry wherewithal as; eit are idriveu to any considerable rdepthiit issues.-

tom-airy to timber the side walls and use either wooden guide rails. or steel railslfor guiclirrgthe ase and heretofore it has been thought neces: sary. in connection wi h the signalling systems in use at the present'time, to'insulate the cage so far as. possible to preserve theiint rity .o f h signaltransmitted. aloft. ;Bu ue h impossi ility of maintainin such insulation, and limther in. preventin variations in the capacityloe tween( he ca e and shaft walls at variouspoints, .as'the cage descends or ascends, changesiin signal streng h-frequently occurred when thecaeeccmes contact with. or is in new contact withthe s a ereby short .circuiting the. oscillator utpu ,.or partiallyshort circuitiugsuch signalsendling circuit. ilhmanyiustances. especially in wet and 'clirtyshaitsirhave found. that wherethe cage 'touchesjthe Sideei the shaftithat the,..s i gna1 .is rendered eitherjfaiut. .Qr unintelligible, or onliterated.

"'Inrcarryine' out mypresent. iuvention I take .advantage olfithe existing capacity which is. always P sent between the case Ill and the walls of th shaft iii in whichis is. suspendedand.utilize'the length. ofithe wire hoistin cable l2 asan autotranslformer, its upper end being grounded hrou h the. sheaves "l3. and their hearings'axid the .metalparts of "the -..housing machinery, .as indicated .at it 4. A radio .frequeucy .osc'illator .15 is carriedon 'the.c.age- All. This maylba of-any suitable.coristructiomsuchas thecirouitshown in .Eig.'2 and, thereforerequires no detail description, sate referenceltoithe primary winding .16 and-the secondary winding 1], which may .be elements of an .output. transformer. iThe outputlls controlled by. a. hand operated plunger .29 by means or whichv a .ncrmallyhpeuset.ofspring contacts 12.! may be closed when a. signal impulse iistoihesent.

..One=.of theterminals ,ofthe, secondary winding lccnnectto cage. .111, as indicated.at zzand the .other'lattach.directly .t0,.-.the cable... asindicated .at .123, .in a. :pos'ition -elevated fromten to twenty .fet.above. the cageptheidi tance beinesuehthat the impedancehetween. the. points cf: connection is-..eq l,livalent to, that ofthe coil. Since the output radio frequenciesof the oscillatorJmay belof earr'crdereof irom .l0.Q-;-ko.-t0 5.00. kc. .it will beep- .preciated that-thesectiou-of, .cablerbetween poin s .22 and 22.4%, ofiers a censiderable impedance and hence there-exists het rzeenethem anappreeiahle -v.o age-which Lam ables-t9 utilize. .I- havefeun'd i inapractiee that'ra turn two-inch.- .coiLsas-the .-.s.eeendary l1. .is--,quite satisfactory-tin QP m i n and. thateitsi pedance may be closely mateheq to that of the intervening section 12 of the cable I2, between points 22 and 23, by adjusting the terminal 23 either up or down, however, experience indicates that this matching of impedances is not critical.

From the above described connections it will be observed from the capacitance, indicated in dotted lines at 25, existing between the cage and walls of the shaft, that a radio frequency signal circuit is completed throughout the length of the cable, even under conditions of perfect insulation of the cage, which circuit is improved in transmission qualities in the event the cage happens to be grounded or partially grounded.

In Fig. 3 I have shown a conventional receiver 30 to which signals are fed from a loop antenna 3| preferably located adjacent the upper end of the cable at the mouth of the shaft and between the latter and the sheave l3. It is understood that the modulated radio frequency currents picked up by the loop are, after amplification detected and thereby stepped down to audio frequency for broadcasting by a loud speaker 32 located in the vicinity of the operator's position on the hoist stand.

Herein I have referred to the suspension end of the hoist cable acting on the principle of an autotransformer since it is possible to comprehend how by a proper choice of circuit parameters a matched condition can be obtained between the generator l5 and transmission circuit existing between any and all parts of the cable and the ground return path formed by the shaft walls resulting in an efilcient transfer of energy which can be picked up at the mouth of the shaft. Another and equally accurate concept of my invention may be had by recognizing that the cable l2 extending centrally of the shaft H becomes a central or coaxial conductor with the earth comprising the outer or surrounding conductor. Thus it will be seen that the capacitance between cage l0 and earth, anywhere in the shaft, is at all times and under all conditions an effective by-pass condenser at the modulated radio frequency used. Hence matching the oscillator to the coaxial transmission line is accomplished by tapping the inner conductor, as at the point 23, so that impedance is presented to the coupling coil II. If the coupling coil impedance is the same as that at the point of said tap a maximum transfer of energy occurs which exists throughout the length of the cable. This impedance I adjust with the cage ill at or near the bottom of the shaft ll, wherever the signal strength appears to be the weakest, presumably at a nodal point, and while it is recognized, theoretically at least, that the impedance at the tap point will change as the cage ascends and the cable length decreases this, from a practical standpoint, is often times immaterial. This impedance change exists because of the standing wave effect produced in the transmission circuit and I have found that because said circuit is very lossy and because the total footage depth of most mine shafts is only a small fraction of a wave length at the radio frequencies employed,

said wave effect is not large.

In cases where the depth of a mine shaft is an appreciable fraction of the radio frequency wave length used and the resulting attenuation between the cage and surface receiver is therefore comparatively large the standing wave effect 'is used to advantage. The oscillator and the tap point on the cable in this case are adjusted to provide maximum transfer of energy for the rethe bottom of the shaft. This assures a more constant radio frequency signal to the receiver on the surface because the transfer of energy from the oscillator to the transmission path is most efficient when the cage is near the bottom of the shaft when the attenuation isthe largest, there being no diminution of the signal, as will be understood, when the cage rises. As the cage rises the attenuation becomes less and the energy required becomes correspondingly less.

This decrease in the transfer of energy is brought about by the change in the oscillator load impedance as the cage rises.

One of the advantages of the circuit arrangement above set forth is that I am able to impose the radio frequency signalling energy upon the cable at a point between the cage and the upwardly extending length of cable without physically parting the cable and depending upon the imposition of an insulator as a means of suspending such lower end of the cable with the cage suspended thereon.

Another advantage that will be appreciated in mine workings is that I am able to completely obviate the use of circuit conductors leading upwardly from the cage which must needs be wound and unwound as the cable is shortened and lengthened and yet assure a proper transmission of signals under the worst operating shaft conditions that may exist.

I claim:

1. In a mine shaft signalling system comprising a hoisting cable and a cage suspended thereon, of a radio frequency oscillator carried on the cage having primary and secondary output transformer coils, the terminals of the secondary coil bridging a section of the said cable adjacent the cage and substantially matching the same to the impedance of said section, and a modulated radio frequency receiver having a pick-up circuit associated with the upper end of the cable.

2. In a signalling system for use in mine shafts, the combination with a hoisting cable having loss electrical transmission characteristics and a cage suspended thereon, of a modulated radio frequency generator having an output feeding into the lower end of the cable and comprising an impedance matched to the circuit formed by the cable and the return ground path through the shaft walls, and a receiver having a circuit associated with the upper end of the cable for detecting said frequencies directly therefrom and rendering the same distinguishable.

3. In a signalling system for use in mine shafts, the combination with a hoisting cable having a cage suspended thereon, of a radio frequency generator having an output coil the terminals of which are in electrical communication with two difierent points at the lower end of the cable which are separated a distance to match the impedance of the intervening cable section to that of the coil and render the remainder of the cable an autotransformer of impressed signals, and a surface receiver of modulated radio frequency signals comprising a secondary winding associated with the upper end of the cable receiving the current variations therein.

4. In a signalling system for use in mine shafts.

the "combination with a hoisting cable having a cage suspended thereon, of a radio frequency generator on the cage having an output coil the terminals of which are in electrical communication with two different points at the lower end of the cable, one'of said terminals being adjust- 6 I able longitudinally of the cable to match the im- REFERENCES CITED pedance of the intervening section of the cable The following references are of record in the to that of said coil thus rendering the upwardly file of this patent: extending portion of the cable an autotransformer for impressed radio frequency signals, 5 UNITED STATES PATENTS and a surface receiver of modulated radio fre- Number Name Date quency signals comprising a secondary winding 1,098,528 Reineke June 2, 1914 associated with the upper end of the cable re- 1,739,613 Russey Dec. 17, 1929 ceiving the current variations therein. 2,001,847 Lockrow May 21, 1935 RICHMOND L. RUTHERFORD. 10 2,248,825 Rutherford July 8, 1941 2,368,532 Fearon Jan. 30, 19 15 

